The invention relates to a steering column for a motor vehicle, which is at least adjustable in its longitudinal direction. The steering column comprises a support unit connectable with the chassis of the motor vehicle, a setting unit rotatably bearing supporting a steering spindle, and a clamping mechanism. In the opened state of the clamping mechanism, the setting unit is at least displaceable with respect to the support unit in the longitudinal direction of the steering column and, in the closed state of the clamping mechanism, the set position of the setting unit in normal operation is secured in position with respect to the support unit. The clamping mechanism comprises at least one arresting part which, in the closed state of the clamping mechanism, is tightened together with an engagement element and, in the opened state of the clamping mechanism, is spaced apart from the engagement element. The setting unit is connected with the engagement element so that the setting unit in normal operation is held nondisplaceably in the longitudinal direction of the steering column with respect to the engagement element, and in the event of a crash is dislocatable in the longitudinal direction of the steering column with respect to the engagement element with the absorption of energy.
Steering columns which are adjustable for the adaptation of the position of the steering wheel to the seating position of the driver are known in various embodiments. Apart from adjustable steering columns which are only adjustable in length or height and inclination direction, respectively, steering columns are known which are adjustable in length as well as also in height and inclination.
As a safety measure in the event of a vehicle crash, it is known to realize the steering column in a section adjoining the steering wheel-side end such that it is displaceable in the longitudinal direction of the steering column with the absorption of energy. A conventional form of implementation provides for this purpose that the support unit, with respect to which the setting unit in the opened state of the clamping mechanism, which unit rotatably supports the steering spindle, is adjustable for setting the position of the steering column, is connected with a chassis part applied on the vehicle chassis such that it is displaceable with respect to the chassis part under the consumption of energy. Such a design is disclosed, for example, in U.S. Pat. No. 5,517,877 A.
DE 28 21 707 A1 discloses a non-generic, since not adjustable, steering column, in which the jacket tube rotatably bearing the steering spindle includes bilaterally projecting lobes, which lobes are connected by means of securement blocks and bolts penetrating therethrough on the chassis. In the event of a crash, the lobes can become detached from the securement blocks whereby a dislocation of the jacket tube becomes possible. Herein, between the securement blocks and the lobes, U-shaped bending strips are provided on which, during the dislocation of the jacket tube, deformation work is carried out. The bending strips are herein enclosed in chambers of the lobes and are in contact on opposing side walls of the chamber such that the rolling radius of the particular bending strip is limited and predetermined in its deformation.
An adjustable steering column comprising a setting unit rotatably supporting the steering spindle and a support unit, with respect to which the setting unit, in the opened state of a clamping mechanism, for setting the position of the steering columns is at least adjustable in the longitudinal direction of the steering column, is disclosed in EP 0 598 857 B1. In the event of a crash, the setting unit can become dislocated in the longitudinal direction of the steering column with respect to the support unit or a clamp bolt of the clamping mechanism. For the energy absorption bending strips or bending wires are provided entrained by the setting unit and placed about the clamp bolt, which are deformed. A disadvantage of this solution is that the possible dislocation path or the characteristic of the energy absorption in the case of this device depends on the particular set length of the steering column.
U.S. Pat. No. 5,961,146 A, further, discloses a non-generic steering column adjustable only in the height direction in normal operation. Similarly to the manner previously described, about the clamp bolt of the clamping mechanism is provided a U-shaped curved bending wire, which, in the event of a crash, is entrained by the setting unit becoming dislocated with respect to the clamp bolt in the longitudinal direction of the steering column, wherein bending work is performed.
A steering column of the type described in the introduction is disclosed in WO 2007/048153 A2. In the closed state of the clamping mechanism, the engagement element is prevented by the arresting part of the clamping mechanism from becoming displaced with respect to this arresting part. The setting unit can become displaced with the absorption of energy with respect to the engagement element in the longitudinal direction of the steering column. For the absorption of energy, a bolt is disposed on the engagement element, which bolt projects into an elongated hole of an energy absorption part disposed on the setting unit, and during its dislocation in the event of a crash widens this elongated hole. To attain a defined energy absorption, the material properties of the energy absorption part must, in reproducible manner, be precisely fixed in the proximity of the elongated hole.
Similar steering columns are also disclosed in EP 0 849 141 A1 and EP 1 464 560 A2. The engagement elements are guided such that they are displaceable in the manner of a carriage by guidance parts in the longitudinal direction of the steering column, wherein they are retained under friction closure with respect to the guidance parts or deform these parts with the consumption of energy. In the case of a friction-closure retention, the clamping force of the clamping mechanism enters into the extent of the energy absorption and with a plastic deformation of the guidance parts, their material properties must be realized such that it is reproducible in a precisely defined manner.